The present invention relates to a push button switch that has simple structure and having an override interruption structure so as to automatically open the circuit in case of the override.
Many conventional push buttons with an override interruption structure known to applicant are disclosed in U.S. Pat. Nos. 5,786,742, 5,223,813, 4,937,548, 4,661,667, 5,223,813, 4,931762, 5,451,729 and 4,704,594. U.S. Pat. No. 4,937,548. A thermally deformed bimetal plate is used to open circuit in case of the override. However, the action to open the circuit takes time because the structure for disengagement two contact points is indirectly operated by the bimetal plate so that there is a possibility that the electric current will destroy the electric equipment in case of the override. Furthermore, an additional wire is required between the bimetal plate and a conductive plate. In U.S. Pat. No. 5,786,742, the button is directly connected to the contact point so that the open action for the circuit is not fast enough to timely protect the equipment.
The present invention intends to provide a push button switch that has a simple structure and timely opens the circuit to protect the electric equipment.
In accordance with one aspect of the present invention, there is provided a push button switch comprising box having a button movably inserted in an open top of the box. A tubular member extends from an underside of the button and a spring is biased between the tubular member and the box. A tongue extends from an underside of the button and a recessed area is defined in a surface of the tubular member. The recessed area has a polygonal inner periphery and a central member is located in a center of the recessed area. A first terminal plate and a second terminal plate respectively extend from a bottom of the box. A board extends from an inner side of the box and a hole is defined in a surface of the board. Two rods respectively extend from the inner side of the box.
A movable member has two slots and the rods are movably received in the two slots. A U-shaped member has a leg extending through the movable member and engaged with the recessed area. The other leg of the U-shaped member is inserted in the hole in the board. A U-shaped bimetal plate has a central plate located between two legs of the U shaped bimetal plate and a first contact point is connected to the central plate. The two legs of the bimetal plate is fixedly connected to a top of the first terminal plate. The bimetal plate is located beside an end of the movable member. An oscillation member has a first end pivotally connected to the second terminal plate and a second end of the oscillation member has a second contact point connected thereto. A curved spring has an end fixedly connected to the box and the other end of the curved spring is connected to the oscillation member. The tongue contacts the curved spring.
The object of the present invention is to provide a switch that has a movable member which is pushed by the bimetal plate in case of the override and the movement of the movable member shifts a U-shaped member to let the button to jump up.
These and further objects, features and advantages of the present invention will become more obvious from the following description when taken in connection with the accompanying drawings which show, for purposes of illustration only, several embodiments in accordance with the present invention.